Crushed-rock embankment is a main cooling measure in permaf rost regions along the Qinghai-Tibet Railway. An accurate description of airflow within crushed-rock layer is a key in numerical analysis of the cooling effects of crushed rock embankment . A wind tunnel experiment is carried out to investigate the relationship between the seepage velocity and the pressure gradient within crushed rock layer . In the experiment , the mean particle size of t he crushed rock is 12. 5 cm with a porosity of 0. 487. The pressure gradient sand the seepage velocities in t he crushed rock layer are measured under different outside wind speeds.The experimental results show that the seepage velocity increases nonlinearly with pressure gradient ,and t heir relationship can be well-expressed by the Forchheimer equation. In addition , the permeability and the inertial drag coefficient of t he crushed  rock layer are obtained based on the Forchheimer equation. The study provides a scientific basis for numerical analysis of the cooling effect s of crushed  rock embankments with different structures.